A subterranean gas or oil well typically begins with a hole bored into the earth, which is then lined with joined lengths of relatively large diameter metal pipe. The casing thus formed is generally cemented to the face of the hole to give the well integrity and a path for producing fluids to the surface. Conventionally, the casing and cement are subsequently perforated with chemical or mechanical means in one or more locations of the surrounding formation from which it is desired to extract fluids. In general, the perforations extend a short distance into the formation. One of the problems inherent in the art is in maintaining a balance between perforation size and spacing and the required structural integrity of the casing.
Much effort has been devoted to developing apparatus and methods of perforation. Explosive charges are sometimes used to construct perforating guns, such as disclosed for example in, U.S. Pat. No. 5,701,964 to Walker et al. Problems exist with explosive perforation devices. The physical size and arrangement of the perforating gun are often constrained by the tubing size. For example, in the perforation of a five inch diameter casing, it may be necessary for the perforating gun to pass through one and eleven-sixteenth inch diameter tubing. The limited size of the perforating assembly creates problems in orienting the charges to achieve the desired perforation density and pattern.
Attempts have been made to increase the effectiveness of explosive perforation methods by combining them with propellant fracture devices. An example of such attempts is disclosed in U.S. Pat. No. 5,775,426 to Snider et al, wherein a sheath of propellant material is positioned to substantially encircle at least one shaped charge. Under this method, the propellant generates high pressure gasses which clean the perforations left by the explosive charge. This method and apparatus suffers from limitations imposed by physical size restraints similar to those discussed above.
It has been observed that the use of explosive charges to perforate a well can cause additional problems resulting from the damage to the formation. Damage to the formation can restrict the flow of fluids into the well. Formation damage due to explosive charges also produces debris which can then be carried by fluids into the production stream. Additionally, explosive perforation can perforate control lines, requiring repairs before production can begin.
A production issue closely related to perforation is sand-control. The introduction of particles larger in cross section than a chosen size, whether sand, gravel, mineral, soil, organic matter, or a combination thereof into the production stream of the well commonly occurs, requiring methods of sand-control. The introduction of these materials into the well often causes problems, including plugged formations or well tubings, and erosion of tubing and equipment. There have therefore been numerous attempts to prevent the introduction of sand and gravel into the production stream.
A common method to prevent the introduction of sand and gravel into the production stream has been the use of a sand-control screen. In general, this involves placing a sand-control screen jacket assembly between the wellbore and a base pipe. The sand-control screen jacket assembly is designed to allow well fluids to flow into the base pipe while excluding other material. Many variations of sand-control screen jacket assemblies exist, including a radially expandable sand-control screenjacket assembly. The methods of using, a radially expandable screen jacket assembly includes causing the radial expansion of the base pipe and surrounding screen jacket assembly by drawing a mechanical expansion tool through the base pipe. Attempts to perforate a well containing a sand-control screen jacket assembly have the added problem of avoiding failure of the screen during the perforation operation.
Most perforating prior to sand control is conducted with tubing-conveyed perforating guns. This allows the perforation hole size and shot density to be maximized as well as allowing the well to be perforated in an under-balanced condition. Perforating in an under-balanced condition causes the formation fluids to surge into the wellbore yielding a cleaning effect. After perforating in an under-balanced condition the well must be xe2x80x9ckilledxe2x80x9d by circulating out the produced fluids and replacing them with heavier completion fluids. The perforating guns are then pulled from the hole and a completion packer and sand control equipment is run into the hole. During the pulling of perforating equipment and running of completion equipment it can be very difficult to control completion fluid loss into the formation. Oftentimes significant amounts of fluid are lost to the formation, which can be expensive and potentially damaging to productivity. Fluid loss pills are often required, which also can be expensive and damaging.
Some efforts have been made to combine well perforation and the use of screen assemblies in one operation. U.S. Pat. No. 5,845,712 to Griffith Jr. is an example of such apparatus and methods. The apparatus and methods involve perforating and gravel packing a well section in one downhole operation, or trip. The inventions and disclosures of U.S. Pat. No. 5,845,712 are incorporated herein for all purposes by this reference. These methods continue to have the above-mentioned problems associated with physical constraints imposed on explosive charges, and with the need to balance structural integrity of the well casing and screen assembly with useful perforation.
Due to the aforementioned problems associated with the perforation of a well casing and formation, and with the related problems of introducing sand and gravel into the production stream, a need exists for apparatus and methods providing improvements in perforation and associated sand-control.
The invention provides apparatus and methods for perforating a subterranean well. In general perforating apparatus, including a pre-weakened casing apparatus and a propellant assembly, is deployed within a formation of the well. Activation of the propellant assembly fails the pre-weakened casing apparatus perforates and the well formation.
According to one aspect of the invention, the pre-weakened casing apparatus has substantially orthogonal notches.
According to another aspect of the invention, the pre-weakened casing apparatus has notches in its inner surface.
According to yet another aspect of the invention, the pre-weakened casing apparatus has substantially conical notches.
According to another aspect of the invention, a sand-control screen jacket assembly is deployed in the well with the perforating apparatus.
According to still another aspect of the invention, perforation and sand-control steps are accomplished in a single trip.